It is known that tissue, including damaged myocardial tissue, can be ablated by the application of radio frequency energy thereto via conductive electrodes embodied in a probe structure. RF ablation of tissue is commonly used in an attempt to remove myocardial defects, tumours, portions of tissue mass, and the like. RF ablation can be used to treat cardial disfunctions such as ventricular arrhythmia, atrial flutter, atrial fibrillation, ventricular tachycardia and the like.
Such disorders involve abnormal heart muscles causing abnormal activity of the electrical signals that are generated to create muscle contraction. One result of this abnormal electrical activity in the atrial part of the heart muscle may be an irregular heartbeat. A common feature of atrial fibrillation is impaired atrial contraction. The heart beat rate may also be increased.
Electrode catheters are commonly used to effect RF ablation of tissue to remove or otherwise interrupt the abnormal electrical activity caused by defective myocardial tissue.
FIG. 1 is a schematic diagram illustrating such a catheter 10. The catheter 10 is typically made of a highly flexible plastic or rubber tube 14. At the distal end of the catheter body 14 are located a number of metal electrodes 12 for delivering RF energy. The conventional catheter probe utilises ring-like electrodes concentrically arranged around the catheter body 14. Alternatively, the catheter probe 10 alone or in combination with the ring-like electrodes may have a single electrode at the tip of the distal end of the catheter 10. The catheter body 14 includes a number of internal electrical conductors (not shown) connected to respective ones of the electrodes 12 at one end. The conductors can be connected at an opposite end of the catheter 10 to a source of RF energy and other equipment. The RF energy is delivered via the conductors to the electrodes 12.
In use, such a catheter probe 10 is inserted via an incision in a patient's body into a blood vessel, such as a vein, and the catheter is then manoeuvred through the blood vessel to the patient's heart. Thus, the electrodes 12 at the distal end of the catheter 10 can be inserted into an interior chamber of a patient's heart to ablate endocardial tissue. FIG. 2 is a simplified schematic diagram illustrating the catheter 10 disposed within a portion of an atrium 20. A defective portion of the myocardial tissue is detected by mapping electrical activity in the myocardial tissue, and then applying RF energy via one or more of the electrodes 12 adjacent to the defective portion.
A significant disadvantage of conventional catheter ablation is that, due to the very flexible nature of the catheter itself, it is difficult to accurately position and maintain the positioning of the electrodes relative to a portion of myocardial tissue. This is disadvantageous in that movement and imprecise placement of the catheter can result undesirably in the ablation or destruction of healthy tissue, while at the same time the tissue sought-to-be ablated may not have been ablated, thereby requiring further ablation.
As will be understood from FIG. 2, due to the readily flexible nature of the catheter body 14 and its limited ability to retain any particular form, the catheter 10 is difficult to position at a desired location, and often does not adequately conform to the tissue surface. As shown in FIG. 2, due to contact with a far wall of the atrium, the catheter body 14 flexes upwardly from its insertion at left into the atrial chamber and is then bent downwardly at its distal end by the irregularity 22 in the myocardial tissue of the atrium 20. Due to the way in which the catheter 10 is bent and its imprecise positioning, only a small portion of the distal end of the catheter 10 contacts the tissue at location 22. In fact, only a small portion of the third electrode contacts the defective, irregularly shaped tissue 22.
Another disadvantage of such catheter probes 10 is that they are directed to ablating focal defects, where only a portion of an electrode in contact with the tissue produces a “spot” or pointlike lesion in the tissue.
A further catheter ablation probe has been proposed using the same type of highly flexible catheter structure in combination with an external guide wire provided between the distal end and an intermediate point of the catheter probe. The guide wire can be tightened or released so as to control arcuate flexing of a sequence of band-like electrodes arranged along the catheter. However, this probe is also disadvantageous in that movement and placement of the catheter is still imprecise and the electrodes may not have good contact with irregular surfaces to be ablated. Still further, the ring-like electrodes of such a catheter probe also produce a “spot” or pointlike lesion in the tissue.
Thus, conventional catheter probes have a number of significant disadvantages. Firstly, the electrodes of the probe are directed to producing spot or pointlike lesions in tissue. Secondly, due to the highly flexible nature of the catheter body, it is difficult to manoeuvre and accurately position and retain the position of the electrodes of the catheter at any position. Thirdly, again due to the very flexible nature of the catheter typically made of soft, bendable plastic, or rubber like substances, the distal end of the catheter does not readily conform to irregularly shaped surfaces of tissue. Accordingly, a need clearly exists for a probe capable of overcoming one or more disadvantages of conventional devices.